A communication system shown in FIG. 1 is known as a conventional communication system. FIG. 1 is a diagram showing conventional communication system 1. Communication system 1 in FIG. 1 is mainly formed of radio base station apparatus 2, main unit 3, and a plurality of handsets 4. A plurality of handset 4 define single cell #10.
In communication system 1 in FIG. 1, radio base station apparatus 2 transmits a downlink signal to main unit 3 and main unit 3 splits the downlink signal and distributes the downlink signals to a plurality of handsets 4. Each handset 4 then transmits the distributed downlink signal to a terminal (not shown) in single cell #10 by radio. A plurality of handsets 4 each receive an uplink signal which is a radio signal transmitted from a terminal (not shown) in single cell #10 and transmit the received uplink signal to main unit 3. Main unit 3 then transmits the received uplink signals to radio base station apparatus 2. Accordingly, conventional communication system 1 can secure a wide coverage in proportion to the number of handsets since a plurality of handsets 4 define single cell #10.
The need for improving a user throughput in packet data communication has been increasing in recent years in addition to the need for securing a wide coverage. A communication system defining only a single cell shown in FIG. 1 finds it difficult to meet this need. For example, a problem arises in a situation where a user performing communication involving a high occupancy rate of a radio band shared by a plurality of users exists in a single cell. In this situation, the throughputs of users communicating in the same single cell as the single cell used by the user are lowered.
The system configuration shown in Patent Literature 1, which uses different communication systems in combination, may be employed as a communication system to solve the problem. According to Patent Literature 1, the system configuration allows the user's in the different communication systems to coexist, thereby solving the above problem.